We propose to continue to isolate and characterize "tumor host range" (THR) mutants of polyoma virus in efforts to identify and characterize the cellular targets of the viral T (tumor) antigens. The rationale behind this selection is that tumor cells may have undergone the loss of particular function(s) which the wild type virus normally targets. These functions may represent tumor suppressor genes or other regulators of replication and survival which the virus needs to inactivate or alter in some manner in order to replicate efficiently. THR mutants are selected to be able to grow on certain tumor cells but not on normal cells and are presumed to have lost the targeting function. One THR mutants has been used to identify the multi-zinc finger homeotic transcription factor Sal2 as a target of the polyoma large T antigen. We have shown that Sal2 acts in some important respects like p53 in terms of its growth arrest and apoptosis inducing properties. In this application we focus on Sal2 with efforts to determine its downstream cellular gene targets, upstream regulators and protein partners. Expression profiling analysis and chromatin immunoprecipitation (ChIP) will be used in these investigations. We will also seek to determine the mutual effects which large T and Sal2 exert on each other based on their interaction. Sal2 is highly expressed in ovarian surface epithelial cells. Preliminary evidence indicates that Sal2 expression is lost in human ovarian carcinomas. We propose to examine further if such loss occurs and at what frequency in various forms of ovarian carcinoma. We will test the hypothesis that promoter methylation in one of the two alternative Sal2 promoters may account for Sal2 silencing in some cases of ovarian carcinoma. Finally, we will take several approaches to developing a mouse model of ovarian cancer based on recent findings on the large T-Sal2 interaction and on the isolation of a new strain of polyoma which efficiently induces ovarian surface epithelial tumors in certain strains of mice.